1. Field of the Invention
The present invention relates to chain door guards.
2. Description of the Prior Art
The provision of a chain door guard which when in use allows a door to be opened a substantial distance, so that the occupant can see and converse with a person outside the door, yet restricting this person from entering the premises, has been known for many years. Such chain door guards enable doors to be opened to an ajar position while still restraining entry of those outside of the door. The conventional chain door guard serves an adequate and useful purpose, however the constructions of these standard units of the prior art allows the door to be opened sufficiently so that there is a space between the door edge and the door casing. A burgler who succeeds in opening a lock which may be present on the door is clearly not adequately restrained from entry into a house or an apartment by a conventional chain door guard, since the spacing present when the door is ajar as restrained by the chain allows a burgler to insert a pry tool or cutting device and thereby to break or clip the chain. Thus it will be seen that it would be desirable to have a chain door guard of such a configuration that a burgler or the like attempting to enter the chain protected area cannot as readily damage or destroy the chain door guard or rip it off from its mounting on the door or on the door casing as can be done to the conventional chain door guard.
In the conventional chain door guard, basically three elements are present. A slide bracket is installed on the interior surface of the door, and this slide bracket is generally horizontally oriented with a horizontal slot therein having an enlargement at the slot end farthest from the edge of the door. The other end of the slide bracket is generally at or near the edge of the door which is juxtaposed with the door casing. The second element in the conventional chain door guard is a chain anchor bracket which is attached to the door casing at a point opposite to the slide bracket. The third basic element in the conventional chain door guard is the chain, one end of the said chain is permanently swiveledly attached to the chain anchor bracket. The other end of the chain has a fitting, known as a coupler or coupling element, extending through the end link so that the coupling element may be inserted into the enlargement at the end of the slot in the slide bracket and thereafter the coupling element may be manually slid along the slot so that the chain is slidably mounted on the slide bracket. It is apparent when the coupling element at the end of the chain is moved to a position in the slot closest to the door casing, there is considerable slack in the chain which allows the door to be opened, possibly of from three to four inches, between the door edge and the door casing. Thus the door can be opened sufficiently for one to see and converse with the person on the outside of the premises, yet offer protection against forced entry into the premises.
However the allowable door opening of the space of 3 to 4 inches has the disadvantage that a burgler who is skilled in opening the door lock can open the door sufficiently with certain tools to cut the chain or even to force pry the chain element loose from the door frame thus gaining free entry into the premises.
Typical prior art in this field will now be discussed. U.S. Pat. No. 3,161,035 deals with a keyed lock member associated with the door frame assembly, whereby the chain assembly can be engaged in the keyed lock member by having the door somewhat open (ajar), so that one can grab the free end of the chain, and enter it into the keyed lock member, then close the door and lock it with the standard lock hardware that the door is fitted with. When unlocking the door, the person would unlock the door first, push it open to the extent the chain would allow, put the key in the door chain lock member, unlock same, and the chain would fall away from the chain lock member, thus freeing the chain from its lock member, allowing the door to be swung fully open and allowing the person to enter the premises.
U.S. Pat. No. 3,275,364 shows a slotted section having an angular hook section fabricated in the slotted section about midway of said slot, with the hook facing forward in the slot member. Thus the chain, upon entering the slot at the enlarged cut out section 10, can move forward without restriction; yet the chain cannot be disengaged from the slot freely unless the coupler element, being spring loaded 25 is depressed manually and slid under the extreme tip of the hook member.
U.S. Pat. No. 3,395,556 deals with a chain lock member which is quite similar to that shown in U.S. Pat. No. 3,161,035 described supra, in addition to which is added the hook member as shown in U.S. Pat. No. 3,275,364 described supra.